Gravity davit and shock absorber therefor



May 27, 1958 J. P. HARKRADER GRAVITY DAVIT AND SHOCK ABSORBE THEREFORFiled NOV. 21, 1955 5 Sheets-Sheet 1 May 27, 1958 J. P. HARKRADERGRAVITY DAVIT AND SHOCK ABSR Filed Nov. 21, 1955 BER THEREFOR 5Sheets-Sheet 2 m. w m m JOHN P #mamans/Q May 27, 1958 J. P. HARKRADERGRAVITY DAVIT AND SHOCK ABsoRBER THEREFOR Filed Nov. 21, l1955 3Sheets-Sheet 3 INVENTOR. Jhw P /MRKRHDER @from/EY United States PatentGRAVITY DAVIT AND SHOCK ABSORBER THEREFOR The invention relates togravity davits of the trackway and pivot types and is applicable tosingle, double or any multiple part fall davits.

Gravity davits of the trackway type may include a davit carriage whichis bodily moveable inboard and outboard on an inclined trackwaysupported on a frame fastened to the ships deck. The carriage supports adavit arm for inboard and outboard swinging movement relative to thecarriage. The carriage is rolled upwardly and downwardly on the trackwayand the davit arm is swung to inboard and outboard positions by thedavit cable or fall which is connected to a winch. Generally, a boat issupported by a pair of such davits. Another form of trackway type davitdoes not include a carriage.

In gravity davits of the pivot type, the davit arm is supported directlyupon a frame structure xed to the ships deck. lnboard and outboardswinging movement of the davit arm is about a fixed axis provided by theframe.

In launching boats yfrom gravity davits of the types described, aportion of the davit arm suddenly strikes with great force the adjoiningsolid stationary frame structure supporting the carriage or davit arm,or the davit frame, supporting the davit arm itself in the case of thepivot type davit. This high energy impact load imposes an unduly highstress upon the adjoining davit frame. In addition, the sudden shock istransmitted through the davit arm to the davit head causing an undulysevere strain to be placed upon the -fall or cable.

When the boat is hoisted inboard on a pair of davits, the davit armssuddenly disengage from their adjoining supporting structures. Thisrarely, if ever, occurs simultaneously. The interval between thedisengagement of the davit arms from their respective adjoiningsupporting structures causes a change in the relative position of theropes or cables so that inboard rotation and movement cannot beaccomplished together or in phase. As a result, the equipment issubjected to excessively high torsion, and the proper functioning of theequipment may be impaired. Moreover, the initial or so-called hump loadincident to initiation of inboard movement of the davits, places anexcessive strain on various parts of the davit, and the davit cable inparticular.

Prime objects of my invention are to dissipate or absorb the high energyimpact load imparted to an adjoining davit frame by a moving `davit arm;to minimize the otherwise excessive strains and twists imparted to theequipment as the davit arm is moved either inboard or outboard; and torelieve the initial hump load, with the attendant excessive strain onthe cable.

In accordance with my invention, the foregoing objects are attained byproviding shock absorber means in combination with existing standardgravity type ships davits, the shock absorber means being so locatedwith respect to the davit arm and its supporting frame structure toafford the most advantageous results.

These and other objects, advantages and results of the fr 2,835,907Patented May 27, 1958 fi vl CC invention will be brought out by thefollowingdescription in conjunction with the accompanying; drawings, inwhich:

Fig. 1 is a side elevational view of one davit of the trackway typeembodying my invention, with the boat and davit arm also being shown inoutboard position as indicated by the dotted lines;

Fig. 2 is a partial front elevational view taken approximately in thedirection of line 2 2 of Fig. 1;

Fig. 3 is an enlarged, partial, side elevational view showing therelationship of the davit arm, its adjoining supporting structure and anintervening shock absorber when the davit arm is in its outboardposition;

Fig. 4 is a partial front elevational view taken in the direction ofline 4-4 of Fig. 3;

Fig. 5 is a side elevational view of a davit of the pivot type embodyingmy invention, the davit arm in its outboard position being indicated indotted lines;

Fig. 6 is a partial front elevational viewtaken in the direction of line6 6 of Fig. 5; and

Fig. 7 is a partial side elevational view showing the relationship ofthe davit arm with respect to its support with an intervening shockabsorber.

Figs. l to 4 illustrate a gravity davit of the trackway type, one davit,generally designated A, for supporting a boat B :being shown. As isusual the boat is suspended from two davits, but since the davits areidentical in construction only one is shown and need be described. Thedavit includes a supporting frame structure comprising a pair of posts10 and 12 mounted on the deck of the ship C adjacent the edge of thedeck and inboard of the deck, respectively. The post 10 may comprise apair of spaced vertically extending members 10, 10', as shown in Figs. 2and 4. Supported by the posts 10 and 12 is a trackway 14 which extendsinwardly and upwardly from the post 10. As known in the art, thetrackway is formed by a pair of spaced and parallel channel bars uponwhich the davit carriage D is mountedfor rolling movement. The davitcarriage is mounted on its inboard end on rollers 16 and on its outboardend is attached to the arm at or near the main rollers 18. Both rollers16 and 1S run on the lower flanges of the channel bars constituting thetrackway. A davit arm E is disposed between cheek plates 2t). The arm isalso provided with rollers 22 that run along the upper sides of the topanges of the channel bars constituting the trackway. The davit armnormally may -be swung inwardly of and seated in the davit carriage withthe rollers 22 engaging the top of the trackway, the rollers 22 actingto hold the davit arm against forward or outboard tilting.

At its upper or head end, the davit is formed with a hook 24 on which issuspended a floating sheave block 26 to which are connected chains orother lines 28 that are in turn connected to the boat B by any knowntype of boat-releasing gear. For hoisting the boat on the davit and forswinging the davit `arm inboard or outboard, a fall line or cable 30 isprovided, one end of which is fast connected to the track frame, asindicated at 32, while the other end is connected to the drum of a winchF. The fall extends from the connection 32 around a sheave 34 (Fig. 2)`at the head end of the davit arm, thence through the sheave block 26,over a sheave 36 on the opposite side of the davit arm from the sheave34, over a sheave 38 on the same side of the davit arm, around a sheave40 mounted on the davit arm, over a sheave 42 on the track frame, andthen to the drum of the winch F. l

In inboard position the boat is provided against lateralH movement inthe davit by the usual Vgripe line 44, one

end of which is fast connected to the trackway, as .at 46 and its otherend connected to the usual takeup and 3 release mechanism 48. The davitis further provided with a boat position bar 50 which is connected by alink to a rig latch hook 52 for releasing the gripe and boat positionbar.

With this construction and arrangement, it will be ap' parent that bytaking up the tall onto the winch, the boat may be hoisted, the davitarm may be swung into its seated position in the carriage and thecarriage and arm may be pulled to its full inboard position as shown byythe solid lines in Fig. l. On its outboard movement, the davit carriageand arm will roll by gravity down the trackway under control of thewinch drum until the outboard rollers 1S engage a stop 14 at theoutboard end of the trackway. Rollers 22 roll along the upper side ofthe trackway, down the face of the stop 14', at which time rotation ofthe arm is initiated in addition to its linear movement. The rotationalenergy is continued after the linear movement is stopped at 14. Thecenter of gravity of the arm and the load being above the pivot axisvprovided by rollers 18, causes additional force or moment tending torotate the arm in the outward direction, 'and thus adds to the energywhich must be absorbed when the rotational movement is stopped suddenly.The davit arm swings outboard to its extreme outboard position shown inFig. 3, and by the dotted lines in Fig. l.

When the davit arm swings to its extreme outboard position, a portion ofthe davit arm, designated 54, below the outboard end of the trackway 14,strikes the davit frame or the supporting posts 1Q, liti with a highenergy impact load. This substantial force is not only applied to thedavit frame, which must be made strong enough to take this blow, but thereacting shock upon the davit arm is transmitted to the davit head, andin turn to the cable from which the boat is suspended. The result is asudden and severe strain upon the cable.

ln accordance with my invention, yieldable shock absorbing means G islocated intermediate the davit arm and the davit trame to absorb ordissipate the high energy impact load imparted by the moving davit armto the frame when the davit arm is rotated to its extreme outboardposition. Any suitable shock absorber, such as a hydraulic or pneumaticor spring unit may be used, the latter being preferred and illustrated.The shock absorber may be secured to either the davit arm or the frame.It is preferred, however, to secure the shock absorber to the stationarydavit frame rather than to the movable davit arm. The shock absorber, orits working face, is located in an outboard direction with respect tothe axis of rotation of the davit `arm for engagement by the davit armwhen the davit arm is in its extreme outboard position. The working faceof the shock absorber is located in a position with respect to the axisof rotation of the davit arm which will best serve to relieve the forceexerted by the davit arm `as it is swung outboard or inboard, takinginto consideration the size of the shock absorber or compression spring.

As shown in Figs. 3 and 4, a spring type shock absorber G is secured tothe davit frame intermediate the posts 1t), 10. The unit comprises aface plate 56 which preferably is convexly shaped to minimize the lareaof engagement when contacted by the davit arm. The face plate isresiliently supported by a coiled compression spring 58, a backing plate60 being located at its opposite end to contain the spring.

In extreme outboard position, the davit arm no longer bears solidly onthe rigid davit frame, but is allowed some restrained movement asindicated by the dotted lines in Fig. 3. The spring is of a size anddegree of compressibility to be only partially compressed when subjectedto peak load s'o that there is always a reserve amount of compression.In other words, the yieldable means G possesses a yielding resistance inexcess ot the pressure exerted thereon through the davit arm by the peakload on the davit arm when the davit arm is at the limit of its outboardmovement. The davit arm may ,4, tinus deflect o1' rotate, therebygreatly reducing or eliminating the effect of the otherwise sudden shockupon the davit arm with the resultingstrain upon the cable.

The described relationship of the shock absorber means with the davitframe and davit arm also has a number of advantageous effects when thedavit arms are being rotated to inboard position. When movement of thedavit arms inwardly is begun, it is practically impossible to initiateinboard rotation and movement of both davit arms simultaneously. At aresult, the relative rope positions on the davits are not the same. Witha shock absorber for each davit located as described, the give ordeliection which it affords serves to maintain the relative ropepositions on both arms. By maintaining the ropes in phase, undue strainsand twists upon the equipment are eliminated.

Another important advantage gained by the described relationship of theshock absorber with respect to the frame upon which it is mounted andthe davit arm movement which it serves to control is to relieve theinitial or hump load which occurs when inboard movement of a davit isbegun. Ordinarily, as rotation of the davit arm is begun, the solidsurface contact between the davit arm and the adjoining solid,stationary frame structure is suddenly broken, thereby causing the fullload to be abruptly taken by the cable or fall 30. As rotation of thedavit arm inboard is continued, the load on the cable decreases rapidlyuntil it may become less than the actual working load. The cable load,however, cannot be allowed to decrease too rapidly, for then the davitwill run away, so to speak. The rotation of the davit must be sufcient,or at a rate, so that when the cable load is reduced by rotation, theload will be in such position that it may be hooked onto the hooks 24.By positioning the shock absorber to be engaged by the davit arm, asshown, contact between the davit arm and the supporting posts is notbroken suddenly. Instead, the davit arm is resiliently supported so thatwhen rotation is begun any lluctuation in load is translated into agradual change of load upon the cable.

As inboard rotation continues from the initial peak or hump load,rotation is about the axis provided by the roller 18, which is nowmoving inboard on the trackway. To provide a shorter lever arm, andthereby decrease the moment of force, a bearing plate 62 is preferablypositioned between the shock absorber and the outboard end of thetrackway 14, that is, between the yieldable means G and the pivotalconnection of the davit arm to the carriage when the davit arm is' inits outboard position. The plate is secured between the posts 10, ld',and is provided with a front bearing surface of convex conliguration tominimize the area of contact with the davit arm.

Figs. 5 to 7 inclusive illustrate the invention as applied to a gravitydavit of the pivot type. A davit arm E', instead of being mounted on acarriage which in turn is moveable upon a trackway, is mounted forinboard and outboard rotation about a xed axis provided by the davitframe, generally designated H. The frame comprises a pair of spacedsupport members 64, 64' secured to spaced, short vertically extendingoutboard and inboard foundations 66 and 68, respectively, fastened tothe deck C. Each support member is formed with laterally spaced inboardinclined plates 70 and 72, the latter being located on the inboard sideof the frame structure. The spaced plates 7i) and 72 are rigidlyconnected to each other at their upper ends by a cross plate 74, and thesupport members 64, 64 are rigidly connected in spaced relation by thetop plate 76. A shaft or axle 7S extends between the inboard plates 72of the spaced support members 64, 64', and is located only a shortdist-ance rabove the foundations. The shaft provides the axis ofrotation for the davit arm E', which is pivotally connected thereto atits lower end.

This davit structure, adapted to launch or hoist a bot B', is providedwith the usual cable, sheaves, winch, gripe line, boat-releasingmechanism, and further includes a torque tube 80 extending to the drum,and a floating coupling 82 at each end to allow for misaligument. A handbrake lever 84 is also provided.

For this type of gravity ships davit, a shock absorber G is mounted onthe outboard side of the frame and is positioned to be engaged by thedavit arm E when the davit arm is swung to extreme outboard position.The shock absorber unit shown is also of coiled compression spring type,and includes a plungerdike element $6 having a face plate 88 `adapted tobe engaged by the davit arm, The relationship of davit frame, davit armand shock absorber provides the advantages hereinbefore described withrespect to the trackway type of davit.

It is believed that the advantages ot' the improved ships davits will beapparent from the foregoing detailed description. It will also beapparent that while the invention has been shown and described in itspreferred form, changes may be made without departing `from the scope ofthe invention as sought to be dened in the following claims.

I claim:

l. A ships davit comprising a supporting frame, a davit arm pivotallymounted on said frame for inboard and outboard rotation, means forsuspending a boat on the davit arm and for controlling inboard andoutboard movement of the davit arm, yieldable means interposed betweensaid frame and the davit arm when the latter approaches the limit of itsoutboard movement, said yieldable means possessing a yielding resistancein excess of the pressure exerted thereon through the davit arm by thepeak load on the davit arm when the davit arm is at the limit of itsoutboard movement, thereby providing yielding restraint of such outboardmovement and relief of the hump load on the davit arm at the start ofthe inboard movement of the davit arm, a track on said frame, a carriagemounted on said track for inboard and outboard movement and to whichsaid davit arm is pivotally connected intermediate the ends of the davit,6. arm, the rst-mentioned means being connected to one end portion ofsaid davit arm at one side of said pivotal connection, and saidyieldable means being interposed between said frame and the other endportion of said davit arm at the other side of said pivotal connectionwhen the davit arm is in its outboard position.

2. A ships davit as defined in claim l with the addition of a bearingplate mounted on said frame between said yieldable means and saidpivotal connection and slidably engageable by the second-mentioned endof the davit arm during inboard movement ot the davit arm from its saidoutboard position, thereby to decrease the moment of force on the davitarm.

3. A ships davit comprising a suporting frame, a davit arm pivotallymounted on said frame for inboard and outboard rotation, means forsuspending a boat on the davit arm and for controlling inboard andoutboard movement of the davit arm, yieldable means interposed betweensaid frame and the davit arm when the latter approaches the limit of itsoutboard movement, said yieldable means possessing a yielding resistancein excess of the pressure exerted thereon through the davit arm by thepeak load on the davit arm when the davit arm is at the limit of itsoutboard movement, thereby providing yielding restraint of suchoutboard. movement and relief of the hump load on the davit arm at thestart of the inboard movement of the davit arm, said yieldable meansincluding a compression spring mounted on said frame.

References Cited in the le of this patent UNITED STATES PATENTS1,190,046 Tjader July 4, 1916 1,237,085 Oliver e Aug. 14, 1917 1,455,159wright May 15, 1923 2,023,258 Young Dec. 3, 1935 2,146,015 HaseltineFeb. 7, 1939 2,411,630 Lehman et a1. Nov. 26, 1946 2,423,876 Dath July15, 1947

